1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to a thin film transistor substrate that simplifies a fabricating method thereof.
2. Discussion of the Related Art
A liquid crystal display device controls the light transmittance of liquid crystal having dielectric anisotropy by use of an electric field, thereby displaying a picture. The liquid crystal display device includes a liquid crystal display panel for displaying picture through a liquid crystal cell matrix and a drive circuit to drive the liquid crystal display panel.
Referring to FIG. 1, a liquid crystal display panel of the related art includes a color filter substrate 10 and a thin film transistor substrate 20 which are bonded together with a liquid crystal 24 therebetween.
The color filter substrate 10 includes a black matrix 4, a color filter 6, and a common electrode 8 which are sequentially formed on an upper glass substrate 2. The black matrix 4 is formed in a matrix shape on the upper glass substrate 2. The black matrix 4 divides an area of the upper glass substrate into a plurality of cell areas where the color filter is to be formed, and prevents light interference between adjacent cells and external light reflection. The color filter 6 has red R, green G, and blue B areas to transmit each of the red, green, and blue lights. The common electrode 8 is formed of a transparent conductive layer formed over the entire surface of the color filter 6 to supply a common voltage Vcom when driving the liquid crystal 24. In order to provide a level surface over the color filter 6, an overcoat layer (not shown) is formed between the color filter 6 and the common electrode 8.
The thin film transistor substrate 20 includes a thin film transistor 18 and a pixel electrode 22 that are formed in each cell area defined by the crossing of the gate line 14 and the data line 16 on a lower glass substrate 12. The thin film transistor 18 supplies a data signal from the data line 16 to the pixel electrode 22 in response to a gate signal from the gate line 12. The pixel electrode 22 formed of a transparent conductive layer supplies the data signal from the thin film transistor 18 to drive the liquid crystal 24.
The liquid crystal 24 having a dielectric anisotropy rotates in accordance with an electric field formed by the data signal of the pixel electrode 22 and the common voltage Vcom of the common electrode 8 to control the light transmittance, thereby realizing a gray level.
The liquid crystal display panel further includes a spacer (not shown) for uniformly maintaining a cell gap between the color filter substrate 10 and the thin film transistor substrate 20. A ball spacer or a column spacer may be used as the spacer.
The color filter substrate 10 and the thin film transistor substrate 20 of the liquid crystal display panel are formed using a plurality of mask processes. One mask process includes a plurality of processes such as a thin film deposition (coating) process, a cleaning process, a photolithography process (hereinafter, referred to as “photo process”), an etching process, a photo-resist peeling process, and an inspection process.
The thin film transistor substrate includes a semiconductor process and requires a plurality of mask processes, thus its fabricating process is complicated and it becomes a major component of the manufacturing cost of the liquid crystal display panel. Accordingly, a thin film transistor substrate has been developed to reduce the number of mask processes from five mask processes.